Ethylene oxide is typically produced by the selective oxidation of ethylene with oxygen in the presence of a silver catalyst. The reaction is exothermic (Δ H250C=−106.7 kJ/mol at 1.5 MPa). In this process, two reactions take place simultaneously at the catalyst surface. In addition to ethylene oxide formation, complete combustion to CO2 and H2O also takes place. This reaction is much more exothermic (Δ H250C=−1323 kJ/mol at 1.5 MPa). Consequently, with decreasing ethylene oxide selectivity, heat generation increases rapidly which makes it difficult to control reaction temperatures. In reverse, higher temperatures result in further decreases in selectivity. This invention provides a solution to these problems.